This invention relates to a process for preparing polyurethane cast elastomers by chain extending an isocyanate prepolymer with 2-methyl-1,3-propanediol.
The casting of polyurethane elastomers in open molds has long been known. E.g., A. Awater, "PU cast elastomers" in Polyurethane Handbook, ed. G. Oertel (New York: Hanser Publishers, 1985), pages 372-388; J. H. Saunders and K. C. Frisch, "Urethane Elastomers" in Polyurethanes, Chemistry and Technology (New York: Interscience Publishers, 1962), pages 273-314. Chain extenders used in the preparation of polyurethane cast elastomers include low molecular weight diamines (particularly aromatic diamines) and glycols (particularly 1,4-butanediol).
It was an object of the present invention to obtain cast elastomers based on glycol chain extenders having improved softness and resilience to compression. It has been found that polyurethane elastomers prepared using 2-methyl-1,3-propanediol as the chain extender are advantageously soft and resilient when compressed, yet are unexpectedly clear and transparent.